https://adobe-type-tools.github.io/font-tech-notes/pdfs/T1_SPEC.pdf,
8.4 First Four Subrs Entries:
"""If Flex or hint replacement is used in a Type 1 font program, the
first four entries in the Subrs array in the Private dictionary must be
assigned charstrings that correspond to the following code sequences. If
neither Flex nor hint replacement is used in the font program, then this
requirement is removed, and the first Subrs entry may be a normal
charstring subroutine sequence. The first four Subrs entries contain:
[...]
Subrs entry number 1:
0 1 callothersubr return
Subrs entry number 2:
0 2 callothersubr return
"""
So subr entry numbers 1 and 2 just call othersubr 1 and and 2, which
means we can just move the handling code over.
No behavior change if flex is used, but more correct if it isn't.
(This only works because our `return` handler is empty, else we would
have to make the callothersubr handler start a call frame.)
0bb8249780